Gene controls brain cell count

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Wouldn't it be fantastic if we could flick a genetic switch and increase the number of brain cells we have? But it would be bad news if this production line ran out of control, because then you'd end up with a brain tumour.

Now researchers in the US have tracked down the gene responsible for maintaining this tricky balance, making sure we grow enough new neurons, but not so many that things get out of hand.

Led by William Snider at the University of North Carolina, the scientists discovered that a gene called GSK-3 controls the signals that determine how many nerve cells we have in our brains. GSK3 is a kinase - an enzyme that sticks little molecular tags on other proteins, switching them on or off to send signals in the cell. They've just published their results in the journal Nature Neuroscience.

The researchers used genetic engineering to create mice whose GSK3 could be removed at a very specific time during the development of the mouse embryo - at a time when a type of brain cell called radial progenitors have just been made. These stem cells produce the bulk of the nerve cells in the brain.

The researchers found that removing GSK3 at this crucial time meant that the progenitor cells were locked into a pattern of constant proliferation, churning out endless new stem cells, rather than mature neurons.

As a next step, the researchers want to find out if adding GSK3 back into the brain after this massive burst of proliferation will make the stem cells mature. They think that they could make mice with three to four times as many neurons as normal mice.

So one day, by manipulating GSK3 levels, we could perhaps increase our brain capacity - Snider describes it as "dialling up and down the number of neurons that are generated in the brain."

The other potentially important thing is that GSK3 has also recently been fingered for a role in a number of psychiatric illnesses, including schizophrenia, depression and bipolar disorder. And lithium,a common treatment for bipolar disorder, works by shutting down GSK3.

The researchers suggest that perhaps doctors should avoid giving drugs like lithium to younger children whose brains might still be growing, in case it causes problems like an overgrowth of cells, which could potentially lead to cancer.